1. Field of the Invention
The invention relates to a grease lubricated ball bearing.
2. Description of Related Art
Grease lubrication has been widely used in the prior art as a method for lubricating a ball bearing. For example, Japanese Patent Application Publication No. 2010-164122 (JP 2010-164122 A) has been proposed for a grease lubricated ball bearing. JP 2010-164122 A discloses a grease lubricated high-speed rotation ball bearing including a plurality of balls, and a circular ring-shaped cage. The balls are interposed between an inner ring and an outer ring. The cage holds the balls at predetermined intervals along a circumferential direction. In such ball bearing, an inner ring shoulder portion is provided on a first axial side of the outer circumference of the inner ring, and a counter bore is provided on a second axial side of the outer circumference of the inner ring. In JP 2010-164122 A, the entire region of the inner circumference of the cage is configured by a cylindrical surface.
An outside diameter of the inner ring in JP 2010-164122 A is smaller at the second axial side than the first axial side. Thus, when the inner ring is rotating, grease flows from the second axial side toward the first axial side in the outer circumference of the inner ring due to a difference in centrifugal force acting between the first axial side and the second axial side in the outer circumference of the inner ring and adhering of the grease in the inner ring. The grease applied to a portion near the outer circumference of the inner ring moves from the second axial side toward the first axial side with such flow. Such grease is desirably guided to the inner circumference of the outer ring, and then, supplied to an outer ring raceway surface.
However, in JP 2010-164122 A, the grease moving from the second axial side toward the first axial side passes between the inner circumferential surface of the cage and the outer circumferential surface of the inner ring, moves to a space located near a first axial side of the cage between the inner and outer rings, and accumulated therein. Therefore, the amount of grease used for grease lubrication between the outer ring raceway surface and the surface of the ball reduces, which may result in poor lubrication.